Damage catalysts

Regeneration of noble metal catalysts to remove coke deposits can successfully restore the activity, selectivity, and stabiUty performance of the original fresh catalyst (6—17). The basic steps of regeneration are carbon bum, oxidation, and reduction. Controlling each step of the regeneration procedure is important if permanent catalyst damage is to be avoided. 

Support-phase changes or loss of surface area are, of course, irreversible, and replacement of the catalyst may be appropriate. Catalyst damage may take the form of phase changes to the alumina support from gamma to theta or alpha phase. The last is catalyticaky inert because of insignificant surface area. Theta alumina has a low surface area (< 100 /g) relative to gamma alumina (180 m /g) and has poor halogen retention. 

The most important part of an ammonia synthesis plant is the pressure reactor, which is filled with catalyst and in which ammonia formation takes place at temperatures between 400 and 500°C. A maximum temperature of 530°C must not be exceeded, otherwise catalyst damage will ensue. 

Alternative design of a steam reformer contains a spherical type catalyst which itself moves downwards while the process gas flows upwards through the catalyst This method increases the efficiency (smaller residual methane contents). Drawback is a catalyst damage due to the movement. 

The lig t distillate product pump, which supplied lean oil to the absorber, lost suction at startup. Gas from the absorber backed through the lean oil line and traveled into the hydrotreater charge pump, causing it to gas up and lose suction. This resulted in hydrotreater catalyst damage. 

Regenerator doesn t remove ad carbon from the catalyst damaged air grid/insuffi-dent air/excessive regenerator velodty/poor spent catalyst initial distribution/ coarse particles. 

Fluorine and chlorine cause catalyst damage by reaction with silica. 

Unless this section is thoroughly understood, much of the significance of the design procedures that follow will be lost. Many processes can tolerate poorly designed control systems, particularly if they are protected from a rapidly varying load. But most chemical reactors will not. Some need no load upset to break into oscillations sufficiently violent to ruin product, destroy catalyst, damage equipment, and endanger life. 

Removal of carbon monoxide and carbon dioxide by methanation is required for the protection of certain hydrogenation and ammonia synthesis catalysts against rapid deactivation. It is also necessary when the hydrogen is used in hydroprocessing operations because CO2 and CO can lead to temperature excursions and catalyst damage in the reactors. Furthermore, methanation is an essential step in the reaction systems associated with the Fischer-Tropsch synthesis and with the production of synthetic natural gas from liquid hydrocarbons and coal. Grayson (1956) presented a detailed discussion of methanation in connection with the Fischer-Tropsch process. 

Usually, the decrease in temperature does not lead to catalyst damage or loss of selectivity. However, the equilibrium conversion decreases as the temperature decreases, as... 

Elemental analysis of the bulk components in a catalyst is measured by X-ray fluorescence (XRF), which has now replaced traditional wet analysis. If required, electron probe analysis can also provide information on the distribntion of elements in a catalyst particle. Bnlk phases in a catalyst and crystallite size are determined by X-ray diffraction (XRD), as either a routine check or a diagnostic procedure to examine catalysts damaged dnring operation. 

The early proeesses used to hydrotreat naphthas only required single beds, but modem plants treating heavier feeds are more complicated. Several catalyst beds with a variety of catalysts are usually required. Inteibed cooling with cold gas quench or liquid feed may also be necessaiy. Hydrotreating reactions are exothermic and cooling is essential to avoid catalyst damage. 

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